GSR Posted February 18, 2010 Report Share Posted February 18, 2010 Dear all, I tried to build up a circuit which controls current though a DC motor. The motor needs to generate strong torque; and the input power will be battery ~12V 2400mAh battery pack. Previously, the motor has been tested. The peak current needed is 5A@30V for ~1s. Then there will be 1 second break before another peak. My plan is to build up a "capacitor train" which has ~5 "high energy density" capacitors. My circuit will include a boost up circuit to change the 12V to 30V DC and then charge the capacitors. After that, the circuit will control the capacitors discharge the energy to motor in sequence; and it will control the recharge of capacitors. (The circuit has to be as small as possible) my questions is where I can find the small and "high energy density" capacitors for this circuit? Quote Link to comment
Francois Normandin Posted February 18, 2010 Report Share Posted February 18, 2010 Not exactly what you ask for, but I thought I'd mentioned it. If you use a "Spike and Hold" circuit like this one, in conjunction with your 12V to 30V boost circuit, then perhaps you don't need the "high-energy density" capacitors. Diodes and transistors are more compact. This circuit is for operating fast solenoid valves, so it's good for inductive loads like a motor. I guess it all depends on how your boost circuit holds for the duration of the spike... Quote Link to comment
GSR Posted February 18, 2010 Author Report Share Posted February 18, 2010 Not exactly what you ask for, but I thought I'd mentioned it. I think I should explain a bit more clear Requirement: Motor generate strong torque for 1s and then have 1s break Information of the motor: to meet the required torque 5A@30V can do that Constriction: Use ~12V 2400mAh battery pack and the control circuit as small as possible My plan was: boost up 12V to 30V and store the energy in capacitors; a controller will control the discharge the power to motor and recharge the capacitors. My question was: Where I can find the capacitors which is suitable for my project Quote Link to comment
Francois Normandin Posted February 18, 2010 Report Share Posted February 18, 2010 I think I should explain a bit more clear Requirement: Motor generate strong torque for 1s and then have 1s break Information of the motor: to meet the required torque 5A@30V can do that Constriction: Use ~12V 2400mAh battery pack and the control circuit as small as possible My plan was: boost up 12V to 30V and store the energy in capacitors; a controller will control the discharge the power to motor and recharge the capacitors. My question was: Where I can find the capacitors which is suitable for my project Indeed, it was clear the first time... I just don't know enough about capacitors to provide infos about them and I thought I would point in an other direction. I'll let some other guys chip in on this. Quote Link to comment
PaulG. Posted February 18, 2010 Report Share Posted February 18, 2010 Dear all, I tried to build up a circuit which controls current though a DC motor. The motor needs to generate strong torque; and the input power will be battery ~12V 2400mAh battery pack. Previously, the motor has been tested. The peak current needed is 5A@30V for ~1s. Then there will be 1 second break before another peak. My plan is to build up a "capacitor train" which has ~5 "high energy density" capacitors. My circuit will include a boost up circuit to change the 12V to 30V DC and then charge the capacitors. After that, the circuit will control the capacitors discharge the energy to motor in sequence; and it will control the recharge of capacitors. (The circuit has to be as small as possible) my questions is where I can find the small and "high energy density" capacitors for this circuit? Why would you want to use capacitors? Look at using a MOSFET circuit. A FET will most certainly be able to handle the current requirements but it will leave a footprint about the size of a small, surface-mount IC. Quote Link to comment
GSR Posted February 18, 2010 Author Report Share Posted February 18, 2010 Why would you want to use capacitors? Look at using a MOSFET circuit. A FET will most certainly be able to handle the current requirements but it will leave a footprint about the size of a small, surface-mount IC. I want to use capacitors because I need to make sure the power supply is stable for that 1s. The battery power pack may not be able to generate enough current to meet the motor requirement, so I use the capacitors to store enough energy for the 1s usage. The idea is similar to a "flash" in a camera. Quote Link to comment
Francois Normandin Posted February 18, 2010 Report Share Posted February 18, 2010 OK, let's do some maths. If we take 30V x 5A for 1 second, you need 150 Joules of stored energy. Stored energy in a capacitor is W=0.5*CV^2, so you need at least 1/3 Farad capacitor. If you want to keep 5A for the whole second, make sure you have some margin... Check out these puppies. EDIT: I think those are huge... well it depends=> Dimensions: 9"L x 3"W x 3"H Quote Link to comment
GSR Posted February 19, 2010 Author Report Share Posted February 19, 2010 OK, let's do some maths. If we take 30V x 5A for 1 second, you need 150 Joules of stored energy. Stored energy in a capacitor is W=0.5*CV^2, so you need at least 1/3 Farad capacitor. If you want to keep 5A for the whole second, make sure you have some margin... Check out these puppies. EDIT: I think those are huge... well it depends=> Dimensions: 9"L x 3"W x 3"H Thanks! I am trying to look for another information which is the amount of Watts that a 1.5V rechargeable battery can produce. I just read an information which said that a "D" battery can produce 28A. This is too impressive . I am not sure the information is right. However, I only need 4-5 "D" batteries if the information is right Quote Link to comment
GSR Posted February 19, 2010 Author Report Share Posted February 19, 2010 Do you believe this?? Is it just a battery inside the cover???? <h2 class="product_name">Super Capacitor - 10F/2.5V</h2>13x33.5mm http://www.sparkfun.com/commerce/product_info.php?products_id=746 data sheet http://www.sparkfun.com/datasheets/Components/TS12S-R.pdf Quote Link to comment
GSR Posted February 19, 2010 Author Report Share Posted February 19, 2010 I think I found what I need ulta-capacitor Maxwell technology * BCAP0350E250T03 * ~$23 each (sale: rell.com) * 350F/2.5V * max peak current 220A * OD = 33 X L = 62 mm * BCAP0100 P270 * ~$18 each (sale: Tecate Group) * 100F/2.7V * max current 54A * 0.025 kg * OD =25.0 X L=50.0 mm Quote Link to comment
Rolf Kalbermatter Posted March 11, 2010 Report Share Posted March 11, 2010 I think I found what I need ulta-capacitor Maxwell technology * BCAP0350E250T03 * ~$23 each (sale: rell.com) * 350F/2.5V * max peak current 220A * OD = 33 X L = 62 mm * BCAP0100 P270 * ~$18 each (sale: Tecate Group) * 100F/2.7V * max current 54A * 0.025 kg * OD =25.0 X L=50.0 mm But to get your 30 V (actually you should go for some margin) you will need more than a dozen of them in series. Seems very costly to me and it will also reduce the total capacitance accordingly. Ctot = 1 / (1/C1 + 1/C2 + ..... 1/Cn) Quote Link to comment
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